Plane: Addition of missing auxiliary channels on failsafe and k_manual passthrough in normal flight

Unsure if this is a deliberate omission, but auxillary channels denoted 'k_manual' or 'k_flap' are not copied as expected in set_servos(). Also, a number of channels are omitted in the failsafe_check() function, which would be disastrous for some setups in case of failure. Losing flap control on a larger aircraft heightens risk.

The manual passthrough is important in our case as the wiring looms are less complicated if this is implemented, and allow us to change channel functions (i.e flaps from manual to auto) in software rather than in a hardware change.

'k_flap' appears redundant and has no apparent difference to 'k_manual', so is assumed to mirror that functionality.